I have an A5 2 fold template. Mathematically it should mesasure 444mm wide (3 x 148 by 210mm height or 3 x A5 paper) but I have set it to be 441mm as one of the sides (of A5) will be folded into the middle and 3mm allows it to do so without bulging, hope you're with me. The whole doc has 3 columns - 2 which are 148 (A5) but one is 145 (this is the one that will be folded in). My question is how did I set that odd column width! I can't remember how I did it. If I go to layout > margins and columns, in the columns, number field it just says 'custom'. Thanks for your help
The only way I know is manually adjusting the column guides. You can do this by clicking
View / Grids / uncheck Lock Column Guides.
You can then use the Select Tool to move the guides much like any other guide.
As far as I know though, gutters have to remain uniform. If you need a more complicated layout, your best bet may be to manually set your guides.